Insulator

ABSTRACT

An insulator is provided with a housing section integrated with an insulating section at a lower portion thereof. The housing section forms a part of a housing of an acceleration pump. Accordingly, the acceleration pump can be disposed at a space around the insulator, which is conventionally a dead space. Thus, a dedicated space for installing the acceleration pump is not required, which achieves space saving. Further, since the acceleration pump is disposed directly around the insulating section, even when a duct that intercommunicates an insulator leading-air passage and the acceleration pump is used, the length of the duct can be reduced to simplify a structure of the interconnection. Furthermore, since the housing section is integrated with the insulating section, the number of components can be reduced to reduce costs and facilitate assembly of the acceleration pump.

TECHNICAL FIELD

The present invention relates to an insulator used for an engine, and more particularly to an insulator used for a stratified scavenging two-cycle engine.

BACKGROUND ART

In a two-cycle engine, an exhaust port and a scavenging port are opened and closed by a piston. When the exhaust port is opened by descent of the piston, combustion gas is discharged as exhaust gas. At approximately the same time, the scavenging port is opened from which mixture in a crank chamber is delivered into a cylinder through a scavenging passage. Until the exhaust port is closed by the piston, the delivered mixture scavenges combustion gas remaining in the cylinder while a slight amount of the mixture itself is discharged. Accordingly, a slight amount of unburnt fuel in the mixture is discharged with the exhaust gas. Thus, fuel efficiency is deteriorated due to fuel loss, and a complicated muffler structure is required to prevent the unburnt fuel from being discharged outside in view of environment preservation.

In order to solve such a problem, a stratified scavenging two-cycle engine has been suggested. The stratified scavenging two-cycle engine has a leading-air passage communicated with the scavenging passage. Accordingly, leading air can be supplied to an upper portion of the scavenging passage before scavenging, and the supplied leading air initially scavenges combustion gas in a cylinder at the time of scavenging. Consequently, mixture is hardly discharged. Thus, fuel efficiency is enhanced and a complicated muffler structure is not required.

A commonly available engine including the stratified scavenging two-cycle engine is typically driven with lean mixture during idling. However, when the stratified scavenging two-cycle engine is suddenly accelerated from an idling state, leading air from the scavenging passage is initially supplied into the cylinder and therefore mixture having a sufficient fuel ratio is not supplied. Consequently, the lean mixture becomes further lean, which causes acceleration failure or engine stop.

In order to solve the above problem, an accelerator for temporarily increasing an amount of fuel during acceleration is provided (for example, Patent Document 1).

The accelerator as disclosed in Patent Document 1 includes a carburetor, an insulator provided between the carburetor and an engine for reducing heat transmission from the engine, and an acceleration pump connected to the carburetor. An insulator leading-air passage of the insulator and the acceleration pump are communicated with each other by a duct.

Patent Document 1: JP-A-2001-123841

DISCLOSURE OF THE INVENTION Problems to Be Solved by the Invention

However, the acceleration pump is remote from the insulator and the carburetor in the accelerator as disclosed in Patent Document 1. Thus, the acceleration pump requires an installation space that is independent of the insulator and the carburetor, which leads to increase in the size. Also, because the acceleration pump and the insulator are connected by the duct, this connecting structure may be complicated when the acceleration pump is largely remote from the insulator and the carburetor.

An object of the present invention is to provide an insulator capable of simplifying a connecting structure and achieving space saving around an engine.

Means for Solving the Problems

An insulator according to an aspect of the invention includes: an insulating section that is provided between an engine and a carburetor and includes an insulator leading-air passage and an insulator mixture passage; and a housing section that is integrated with the insulating section and forms a part of a housing of an acceleration pump.

According to the aspect of the invention, since the housing section integrated with the insulating section partially forms the housing of the acceleration pump, the acceleration pump can be disposed on a space around the insulator, which is conventionally a dead space. Thus, a dedicated installation space for the acceleration pump can be omitted to achieve space saving. Further, since the acceleration pump is disposed directly around the insulating section, even when a duct that intercommunicates the insulator leading-air passage and the acceleration pump is used, the length of the duct can be reduced. Thus, a structure of the interconnection can be simplified. Furthermore, since the housing section is integrated with the insulating section, the number of components can be reduced to reduce costs and facilitate assembly of the acceleration pump.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view showing a structure around an insulator according to an exemplary embodiment of the invention.

FIG. 2 is a cross sectional view showing the insulator as viewed from a carburetor.

FIG. 3 is an exploded perspective view showing an acceleration pump.

EXPLANATION OF CODES

1: engine, 2: insulator, 3: carburetor, 5: housing section, 6: acceleration pump, 20: insulating section, 21: insulator leading-air passage, 22: insulator mixture passage, 64: housing

BEST MODE FOR CARRYING OUT THE INVENTION

An exemplary embodiment of the invention will be described below with reference to the drawings.

FIG. 1 is a cross sectional view showing a structure around an insulator 2 according to the exemplary embodiment of the invention and FIG. 2 is a cross sectional view showing the insulator 2 as viewed from a carburetor 3. FIG. 3 is an exploded perspective view showing an acceleration pump 6.

As shown in FIG. 1, a stratified scavenging two-cycle engine 1, to which the insulator 2 is mounted, includes an engine leading-air passage 11 communicated with a scavenging passage and an engine mixture passage 12 communicated with a crank chamber. Leading air and mixture are taken in through the passages 11 and 12 in an intake process. The carburetor 3 is mounted to the engine 1 via the insulator 2.

The carburetor 3 includes a carburetor leading-air passage 31 at an upper side thereof, a carburetor mixture passage 32 at a lower side thereof, and a constant-pressure fuel supply mechanism 4 that supplies fuel into the carburetor mixture passage 32 at a bottom thereof. The constant-pressure fuel supply mechanism 4 includes a carburetor constant-pressure chamber 41 defined below a diaphragm 40, a constant-pressure fuel chamber 42 defined above the diaphragm 40, an internal passage 43 that intercommunicates a fuel tank (not shown) and the constant-pressure fuel chamber 42, and a fuel pump 44 provided in the internal passage 43.

The carburetor constant-pressure chamber 41 is communicated with outer air through a communicating passage 410. The constant-pressure fuel chamber 42 includes a needle valve 421 for opening and closing a communicating hole 420 that intercommunicates the internal passage 43 and the constant-pressure fuel chamber 42, and supplies fuel from a fuel supply passage 422 into the carburetor mixture passage 32. The fuel pump 44 vertically moves a diaphragm 45 using pulsatile pressure of a crank chamber transmitted from the engine 1. In other words, when fuel is supplied from the constant-pressure fuel chamber 42 into the carburetor mixture passage 32 through the fuel supply passage 422, the communicating hole 420 is opened by the needle valve 421. Subsequently, the fuel pump 44 vertically moves the diaphragm 45, so that the fuel is supplied from the fuel tank into the constant-pressure fuel chamber 42.

The insulator 2 is made of synthetic resin for preventing heat transmission from the engine 1 into the carburetor 3, and has an insulating section 20 for preventing heat transmission and a housing section 5 integrated with the insulating section 20 at a lower side of the insulating section 20.

The insulating section 20 includes an insulator leading-air passage 21 that intercommunicates the engine leading-air passage 11 and the carburetor leading-air passage 31, and an insulator mixture passage 22 that intercommunicates the engine mixture passage 12 and the carburetor mixture passage 32. As shown in FIG. 2, a pulse-transmitting passage 23 is provided at a lower side of the insulator mixture passage 22. One end of the pulse-transmitting passage 23 is communicated with the crank chamber of the engine 1, and the other end thereof is communicated with the fuel pump 44 of the carburetor 3 to transmit pulsatile pressure in the crank chamber into the fuel pump 44. The insulating section 20 is provided with a first passage 24 extending laterally (the right side in FIG. 2) from the insulator leading-air passage 21. The first passage 24 is communicated with a pipe 25 attached to the insulating section 20, a pipe 52 attached to the housing section 5, and a duct 71 including a tube 70 for connecting the pipes 25 and 52.

As shown in FIG. 3, first connecting holes 26A to 26D are formed on corners of the insulating section 20. A nut 27 is buried between the connecting holes 26A and 26B and between the connecting holes 26C and 26D. Second connecting holes 28A and 28B are formed at positions corresponding to the nuts 27. The insulator 2 is mounted to the engine 1 by inserting screws (not shown) into the first connecting holes 26A to 26D, and screwing the screws into screw holes provided on the engine 1. Also, the carburetor 3 is mounted to the insulator 2 by screwing screws penetrating the carburetor 3 and the second connecting holes 28A and 28B into the nuts 27.

An acceleration pump 6 includes the above-described funnel-shaped housing section 5, a diaphragm 60 supported by a collar-shaped support 50 provided on an inner circumferential surface of the housing section 5, a spring 61 fitted into a spring guide 51 formed on a bottom of the housing section 5 and disposed between the housing section 5 and the diaphragm 60, and a cover 63 fitted into the housing section 5 to hold the support 50 and the diaphragm 60 while interposing a packing 62.

In the exemplary embodiment, a housing 64 of the acceleration pump 6 is provided by the housing section 5 and the cover 63. As shown in FIG. 1, in the housing 64, a negative-pressure chamber 65 is provided by a space partitioned by the diaphragm 60 to accommodate the spring 61, and a pump chamber 66 is provided by a space adjacent to the cover 63.

A second passage 54 (see FIG. 2) communicated with the duct 71 is provided on a base 53 of the housing section 5. A pressure-introducing passage 7 is provided by the first passage 24, the second passage 54, and the duct 71. Negative pressure in the insulator leading-air passage 21 is transmitted to the negative-pressure chamber 65 through the pressure-introducing passage 7.

An insertion port 67 is provided on the cover 63. A projection 46 projecting from the carburetor 3 is inserted into the insertion port 67. The pump chamber 66 is communicated with the carburetor constant-pressure chamber 41 through a communicating passage 68 pierced in the insertion port 67 and a communicating passage 460 formed within the projection 46.

Since the housing section 5 forms apart of the housing 64 of the acceleration pump 6 according to this exemplary embodiment, the acceleration pump 6 is disposed in a space between the engine 1 and the carburetor 3 at a lower side of the insulating section 20, which is conventionally a dead space in which no components are disposed. Thus, in this exemplary embodiment, the acceleration pump 6 is provided by efficiently using such a dead space, whereby space saving can be achieved.

Further, the number of components can be reduced since the housing section 5 is integrated with the insulating section 20, which reduces cost and facilitates assembling operation. Furthermore, the acceleration pump 6 is disposed immediately below the insulating section 20, the length of the duct 71 that intercommunicates the insulator leading-air passage 21 and the negative-pressure chamber 65 in the acceleration pump 6 can be reduced, which simplifies a connecting structure.

In the traditional acceleration pump as described above in the background art, a partition forming member is provided within a housing, and a guide for guiding a spring is provided on the partition forming member. However, in this exemplary embodiment, the spring guide 51 for guiding the spring 61 is integrated with the housing section 5, so that a partition forming member is not required. Thus, the number of components can be reduced and the acceleration pump 6 can be downsized by reducing the housing 64 by an amount corresponding to the omitted partition forming member, whereby further space saving can be achived.

The above-described carburetor 3 and the insulator 2 work as described below.

The carburetor leading-air passage 31 is initially closed in conjunction with a throttle valve of the carburetor mixture passage 32 during idling, so that negative pressure is provided in the leading-air passages 11, 21, and 31 by an intake operation of the engine 1. Thus, the negative pressure is introduced into the negative pressure chamber 65 from the insulator leading-air passage 21 through the pressure-introducing passage 7, and the diaphragm 60 is pulled toward the negative pressure chamber 65 against spring force of the spring 61. However, since the throttle valve is opened when the engine 1 is accelerated, the insulator leading-air passage 21 is opened in conjunction with the throttle valve, so that the negative pressure is suddenly lost.

Accordingly, the diaphragm 60 is instantly returned toward the pump chamber 66 by the spring force of the spring 59, and air in the pump chamber 66 is pneumatically sent into the carburetor constant-pressure chamber 41 through the communicating passages 68 and 460. Then, the diaphragm 40 partitioning the constant-pressure fuel chamber 42 and the carburetor constant-pressure chamber 41 is pushed up, so that fuel in the constant-pressure fuel chamber 42 is pressurized, which increases an amount of fuel supplied into the carburetor mixture passage 32. Consequently, during sudden acceleration, a supply amount of fuel is temporarily increased by the acceleration pump 6 to smoothly accelerate the engine 1. At this time, the inner diameter of the communicating passage 410 that intercommunicates the carburetor constant-pressure chamber 41 and outer air is smaller than the inner diameter of the communicating passages 68 and 460 extending from the acceleration pump 6, so that the diaphragm 40 provided above the carburetor constant-pressure chamber 41 can be reliably pushed up by air pneumatically sent from the communicating passages 68 and 460.

It should be noted that, although the best structure, method and the like for carrying out the invention have been described in the above description, the invention is not limited to the above description. Although the invention is illustrated and described mainly with reference to a specified embodiment, those skilled in the art may modify the exemplary embodiment in shapes, amounts, and other specific arrangements to make a variety of modifications without departing from the spirit and scope of the invention.

Accordingly, the above description limiting shapes, amounts and the like is exemplary description for facilitating understanding of the invention and does not limit the scope of the invention, so that description with names of members without all of or a portion of the limitations such as limitations on shapes or amounts are included in the scope of the invention.

For example, it is not required that the pressure-introducing passage 7 that intercommunicates the insulator leading-air passage 21 and the negative-pressure chamber 65 includes the duct 71. The pressure-introducing passage 7 may be provided by a groove provided on a connecting surface of the insulating section 20 which is connected to the engine 1, a passage provided within the insulating section 20 for intercommunicating the insulator leading-air passage 21 and the groove, and a passage provided within the insulating section 20 and the housing section 5 for intercommunicating the negative-pressure chamber 65 and the groove. With this arrangement, the duct 71 provided outside can be omitted. Further, a connecting structure can be simplified and a space can be saved. Also, the pressure-introducing passage 7 may include a groove provided on a connecting surface of the insulating section 20 which is connected to the carburetor 3.

The acceleration pump 6 is integrated with the spring guide 51 within the housing 64 according to the exemplary embodiment. However, a partition forming member, which is disclosed in Patent Document 1 as described in the background art, may be provided in the housing 64, and the spring guide 51 may be provided on the partition forming member, so that one end of the spring 61 can be supported.

INDUSTRIAL APPLICABILITY

The invention is applicable to a portable work machine such as a blower or a brushcutter as an insulator integrated with an acceleration pump provided between a stratified scavenging two-cycle engine and a carburetor. 

1. An insulator comprising: an insulating section that is provided between an engine and a carburetor and includes an insulator leading-air passage and an insulator mixture passage; and a housing section that is integrated with the insulating section and forms a part of a housing of an acceleration pump. 